Data storage apparatus and method for handling data on a data storage apparatus

ABSTRACT

In an embodiment, a data storage apparatus having a plurality of spare area arrays may be provided additional to remote spare areas or alone and each of the spare area arrays respectively may be assigned to essentially each of a plurality of format features of the data storage medium and thereby serve as a contiguous free region in the user area. As a format feature on a data storage disc comprised by a disc drive may be understood in particular a zone, a track or a cylinder in case of multitude discs, a block on a track or as well a sector.

This application is a divisional of U.S. patent application Ser. No.10/502,526, filed on Jul. 26, 2004, and claims the benefit thereof. Thecontents of U.S. patent application Ser. No. 10/502,526 is incorporatedherein by reference.

The invention regards a method for handling data on a data storageapparatus comprising a data storage medium, the medium having a userarea and a spare area defined thereon, wherein upon detection of adefect on the medium in a first step the data assigned to the defect areallocated and mapped into the spare area. The invention further regardsa data storage apparatus comprising a data storage medium formatted in apre-determined architecture comprising a plurality of at least oneformat feature and having a user area and a spare area defined thereon.

Hard disc based devices recording e.g. multimedia streams likeMPEG-encoded video require real-time file systems for writing the datato a disc and for reading the data back. Real-time file systems try towrite all files in time but sometimes cannot succeed for example becauseof disc problems. Conventionally there are then two options: writing thedata too late, or discarding some of the unwritten data. The firstoption will typically cause buffer overflows for recording, which maylead to a significant data loss. The second option may also result in adata loss. Conventional data oriented operating systems have noreal-time requirements and attend to aim for a maximum data integrity,delaying completion of each command until properly executed.

In particular real-time audio-video applications require guaranteedrequest service times from a hard disc drive. This requirement is notalways fulfilled due to some unexpected delays in service time. Replacedsectors, i.e. data of defect sectors allocated to remote spare areas ona disc are one of the reasons for such delays. The delays mainly resultfrom searching replaced sectors and from accessing the remote spare areato which the defect sector data have been allocated to. Such remotespare area conventionally is located in a track or tracks other than theoriginally accessed track of the defect sector. Therefore, trackswitching as well as seek time causes such delay.

In the U.S. Pat. No. 6,101,619 a scheme is provided to reduce the numberof searches by accessing replaced sectors at preferably later timessubsequent to a usual data access. In the U.S. Pat. No. 5,166,936 or theWO 98/03970 low level formatting of tracks is suggested to build goodtracks of data and to prevent a further access of a defect. Suchmeasures take considerable effort and may only be done in idle time.Moreover such transaction system should be guarded against powerfailures.

Further in the U.S. Pat. No. 6,034,831 it is suggested to write datawhich were originally scheduled to be written to a defective region, toa substantially adjacent non-defective area on the original track, ifthe size of the defective region does not exceed a threshold size and towrite such data to a remote non-defective area outside the originaltrack if the size of the defective region exceeds a threshold size.

This scheme still requires for a track switch and is restricted tolimited threshold size of the defective region the threshold size ispreferably only one sector. Still such schemes are not able to guaranteea request service time in case of an access to a defective region or ablock that contains defect, replaced or allocated sectors.

This is where the invention comes in, the object of which is to specifya method for handling data on a data storage apparatus comprising a datastorage medium, in particular to specify a method for handling data on adisc drive comprising a data storage disc, by which a request servicetime may be guaranteed, even in case of an access to a region at thestorage medium containing defective or replaced sectors. A furtherobject of the invention is to specify a data storage apparatuscomprising a data storage medium, in particular to specify a disc drivecomprising a data storage disc, adapted such that a request service timecan be guaranteed even in case of an access to a region of the storagemedium that contains defective or replaced sectors.

The object regarding the method is solved by a method for handling dataon a data storage apparatus comprising a data storage medium, inparticular by a method for handling data on a disc drive comprising adata storage disc, the medium having a user area and a spare areadefined thereon and wherein upon detection of a defect on the medium ina first step the data assigned to the defect are allocated into thespare area and wherein according to the invention in a further stepinformation is provided about the size of a contiguous free region inthe user area and the data allocated in the spare area are at leastpartially re-allocated into the contiguous free region if the size ofthe contiguous free region exceeds or is equal to a determined thresholdsize.

It was realised, that even if data originally scheduled to a defectregion are allocated or re-placed or re-mapped to a remote spare areathis may cause significant performance losses. Data allocated in aremote spare area will in practice usually not happen at the end of anallocation unit, being the smallest addressable unit in a file system.Desirable would be a scheme capable to allocate or re-map data to theend of an allocation unit. The main idea therefore is to re-allocate andre-map data, which were mapped in a remote or other spare area.Preferably the data are re-allocated on the whole, but at leastpartially into a contiguous free region in the user area if the size ofthe contiguous free region exceeds or is equal to a determined thresholdsize. In practice such re-allocation and re-mapping will happenadvantageously at the end of an allocation unit. Therefore, aperformance loss is substantially reduced by the method proposed. Insummary it is based on the idea to convert data, which were allocated,mapped or placed in a spare area, into re-allocated and re-mapped datain a contiguous free region, preferably in the user area.

Continued developed configurations are further outlined in the dependentmethod claims.

In preferred configuration the information is provided by a hostconnected to the apparatus by an interface. This information is used tore-allocate data mapped in a remote or other spare area into thecontiguous free region. Such information may contain location and sizeof the contiguous free region. It is preferably not necessary to keeptrack of a list of free regions for the entire medium. Efficiently thethreshold size is determined as being essentially equal to the size ofthe largest contiguous free region in the user area. In particular ahost may declare the largest contiguous free region, not just the newlyfreed up region. Advantageously the threshold size may also bedetermined in correlation with one logical consecutive sequence of datamapped in a spare area. This allows for an effective re-allocation ofdata.

In a further configuration also the information may be provided by acontroller comprised by the apparatus. This development makes theapparatus responsible for the full knowledge about defect handling, sothat the defect handling is executed almost solely by the apparatus, inparticular by the controller alone, i.e. the defect handling may be doneon-the-fly without occupying the host. The only information which may beprovided by the host is an information, that a contiguous free regionoccurred.

The file system of the host may do a very similar thing and may actuallyallow to reserve or create more free or spare regions in the user areaif needed. At least the host may find out about mapped sectors in astandardised way.

In a further configuration defect data may preferably be re-mappedand/or re-allocated to a preferred pre-determined address area. Thesimplest approach would be then to simply never review such address areaas long as it is not necessary.

In a further configuration a protocol between the storage apparatus anda host may record information of the re-allocation of data as outlinedabove.

In a preferred continued developed configuration a plurality of sparearea arrays may be provided additional to remote spare areas or aloneand each of the spare area arrays respectively may be assigned toessentially each of a plurality of format features of the data storagemedium and thereby serve as a contiguous free region in the user area.As a format feature on a data storage disc comprised by a disc drive maybe understood in particular a zone, a track or a cylinder in case ofmultitude discs, a block on a track or as well a sector. Since therebyspare sectors may be provided on each track any data mapped andallocated in a remote spare area may be re-allocated within the reach ofeach data transfer access without switching a track. This configurationof the proposed method may be done automatically, i.e. by the apparatus,without the intervention of the host. Also this configuration may bedone on-the-fly since the logical to physical address mapping is done inthe controller of the data storage apparatus. Even if no spare sectorsin the reach of each data transfer access may be available, theconversion of data can still be done automatically.

If such spare array areas should happen to be fully occupied thecorresponding data may also be re-allocated to a contiguous free regionin the user area.

The data are preferably re-allocated by slipping. This means not only ashift in the logical to physical address mapping but also a shift in thecontent of the corresponding sectors. As far as possible data originallyallocated in a remote spare sector are re-allocated to the contiguousfree region in sequential order.

Advantageously in the further step the re-allocation and re-mapping ofdata from a spare area to the user area is repeated until preferably alldata of at least one logical consecutive sequence is re-allocated in thecontiguous free region in the user area. Preferably the data arere-allocated at least in units of an allocation unit. A fullre-allocation of all data of at least one logical consecutive sequenceis aimed for. Thereby performance losses are essentially prevented ase.g. a track switch or a search for data mapped in a remote spare sectoris not necessary.

In a preferred configuration the incorporation of logical blockaddresses is prevented in the error correction code (ECC). In particularthe use of physical block addresses for an error correction code as analternative to logical block addresses is preferred. This avoids theneed for complete formatting or low level formatting of a data storagemedium in case of changes in mapping. By the use of physical blockaddresses the error correction code of each sector must not be updatedaccordingly if any changes are made in the logical to physical addressmapping of the data storage medium as proposed. The use of physicalblock addresses in the error correction code of a data storage mediumallows for frequent changes on the medium in an efficient way.

Further the invention leads to a data storage apparatus comprising adata storage medium, in particular the invention leads to a disc drivecomprising a data storage disc, formatted in a pre-determinedarchitecture comprising a plurality of at least one format feature andhaving a user area and a spare area by which the object regarding thedata storage apparatus is solved. According to the invention in suchdata storage apparatus the format architecture provides a plurality ofspare area arrays, each of the spare area arrays being respectivelyassigned to each of the plurality of a format feature. In particular ina disc drive comprising a data storage disc such format feature may beselected from the group consisting of zones, cylinders and tracks.

Continued developed configurations are further outlined in the dependentapparatus claims.

Advantageously the format architecture provides a plurality of sparearea arrays wherein each of the spare area arrays are respectivelyassigned to each of a plurality of tracks.

Further the proposed data storage apparatus advantageously comprises aread/write-head, a drive to rotate the data storage medium and a servoto move the head, a controller having a control electronics, amicroprocessor and a memory and further an interface for connecting theapparatus to a host.

The invention will now be described with reference to the accompanyingdrawing. The figures of the drawing illustrate in a schematic and notnecessarily scaled form preferred embodiments of the invention comparedto prior art. The figures illustrate in:

FIG. 1: a hard disc drive of prior art;

FIG. 2 a: a hard disc drive of prior art with remote spare areas;

FIG. 2 b: a hard disc drive of prior art with conventional skew;

FIG. 3 a: a scheme of sector skipping and slipping in a preferredembodiment;

FIG. 3 b: an allocation and mapping scheme for a defective sector due toa grown defect into a spare area according to a preferred embodiment;

FIG. 4: an example of repeated partial re-allocation and re-mapping ofgrown defect data originally mapped in a spare area into a contiguousfree region in the user area according to a preferred embodiment of theinvention;

FIG. 5: an example of a further preferred embodiment with regard tonon-remote spare area arrays provided essentially on each track of adata storage disc;

FIG. 6 a: a non-remote spare sector being part of non-remote spare areaarrays on a hard disc drive according to a preferred embodiment;

FIG. 6 b: an extended skew on a hard disc drive taking into accountspare area arrays on each track according to a preferred embodiment.

FIG. 1 illustrates the structure of a hard disc drive 1 comprising adata storage disc 2, a read/write-head 3, a drive, which is not shown,to rotate the data storage disc 2 around a spindle 4 and a servo, whichis not shown, to turn the head 3 around an axis 5 to move the head 3 toa pre-determined position on the disc 2 to transfer data therewith. Thehead 3 is controlled by a read-and-write electronics and a servoelectronics being part of the controller 6 of the disc drive. Thecontroller 6 further comprises a formatter electronics which upon a datarequest converts such request into corresponding numbers of formatfeatures of the disc 2. Such data request may be received from a host 7by an interface and an interface electronics. Further the controller 6comprises a microprocessor, ROM and RAM e.g. a buffer memory.

The disc 2 contains according to a format architecture a plurality offormat features of the kind selected from the group of zones 9, 10, 11each comprising a plurality of tracks 8. A track is divided into aplurality of blocks 12, 13, 14. Preferably all blocks 12, 13 and 14 havethe same size of data capacity. As the number of blocks per track mayvary from to track to track or zone to zone some of the blocks may bedivided by servo wedges 15. Servo wedges may also be evenly spacedradially around the disc like spokes on a wheel. If the disc drive 1should contain multiple heads 3 for multiple discs 2 then the tracks 8of a disc 2 and the corresponding tracks 8 of the further discs being atthe same radius are referred to as a cylinder. In this case each trackassigns a respective cylinder. Further in a conventional drive a remotespare area 16 is provided on the disc 2 as a track or plurality oftracks at the inner circumference of the disc 2. Such remote spare areamay be conventionally also provided as evenly spaced spare tracks atfurther circumferences on the remaining area of the disc.

The number, size and allocation of remote spare areas may be differentfor different hard disc drives depending on the manufacturer and productfamily. For instance there can be a number of remote spare areas 16evenly spaced in the address space as indicated in FIG. 2 a. Also theremay be just one remote spare area 16 located at the inner diameter,outside the user addressable area as shown in FIG. 1.

Each data storage apparatus and in particular disc drive may havedependent on its structure and handling a maximum service time. Themaximum service time of a drive is the total time of the data transferand the maximum access time and can be calculated using the formulaT=AX+B. The parameter A is the transfer time of a single sectorexpressed in time per sector. The parameter X is the number of sectorsto be transferred and the parameter B is the maximum access time whichis the sum of seek time and rotational latency time. Rotational latencytime may in particular but not only result when the read/write-head hasto switch to a next track. In the preferred embodiment of the inventionthe latter may advantageously be restricted to one full rotation.

There are cases where a conventional drive is not able to finish arequest within this maximum service time. Examples of such cases areretries due to an error correction code error, servo errors due toshocks and vibrations and hard errors. Hard errors are caused by mediadefects and are handled conventionally by the defect management of adrive. When an error correction code error cannot be corrected withseveral retries it is possibly caused by a media defect. To verify thatthe error was caused by a media defect, the drive performs a media teston each defective sector. The media test consists ofwrite/read-verifies, wherein the suspicious sectors are written and readseveral times. If any of them fails then the sector is a grown defectand is conventionally allocated to a remote spare sector. FIG. 2 a showsa schematic view of a data storage disc with a head 3 and a plurality oftracks 8 containing two remote spare areas 16.

FIG. 2 b illustrates schematically a conventional track skew 18 of anouter track 8 a adjacent to an inner track 8 b upon an angle 18 incircumferental direction in the direction of rotation 19 of the disc 2.Corresponding first sectors referred to as start sectors of the tracks 8a and 8 b are depicted as 20 a and 20 b.

As shown in FIG. 2 b a track skew may be employed in hard disc drives tominimise rotational latency time. Rotational latency time results whenthe drive has to switch to a next track to access sequential data.Conventionally a skew is large enough to make sure the head 3 has enoughtime on the next track 8 b to settle and to read a position informationafter it is switched to a next track 8 b. Such position informationusually is comprised by a servo wedge 15 on each track. Servo wedges mayalso be evenly spaced on a disc like spokes on a wheel. Therefore, trackskewing provides a mutual shift of corresponding sectors in adjacenttracks in a circumferental direction 19 relative to each other. Due totrack skewing e.g. corresponding sectors of tracks are not localized inradial direction along a straight line but instead along bended lines 17such as depicted in FIG. 1.

Conventionally only during manufacturing defective sectors are skipped.In a preferred embodiment as shown in FIG. 3 a occurring during use ofthe data storage apparatus, known as a grown defect may be a defectivesector 3 replaced by a next immediate spare sector in order to maintainthe sequential ordering of logical data sequences. This techniqueeliminates the need to seek to another track to access a replacement ofan sector allocated in a remote spare area. If defects, known as growndefects, occur during application of a hard disc drive, such skip andslip scheme is applied during an application, in the field, in theembodiment. It is applicable within a wide and unlimited range, as aspare area may be provided, e.g. on the user area or as a spare areaarray in essentially each of a plurality of at least one format feature,e.g. a track. Defects that occur during application are, if found,allocated to a spare sector, remote or non-remote. Afterwards they maybe re-allocated in a contiguous free region on the user area.

In the situation depicted in FIG. 3 b, in a preferred embodiment thephysical sector PBA 3 is allocated to the replacement sector S2 in aremote spare area 16 as e.g. depicted in FIGS. 1 and 2 a. The logicaladdress LBA 3 is mapped to the replacement sector S2. Converting thephysical sector PBA 3 into a slipped sector, is indicated in FIG. 3 a.This allows for not only a shift in the logical to physical addressmapping but also for a shift of a content of the corresponding sectors.In the example of FIG. 3 a this means that the logical block address LBA3 will be mapped on the physical block address PBA 4, LBA 4 will bemapped on PBA 5, LBA 5 will be mapped on PBA 6 and so on. At the sametime the content of PBA 3 which is located at the replacement sector S2has to be re-allocated from S2 to PBA 4 and the content of PBA 4 can bemoved to PBA 5 and so on. This slipping in the field should continueuntil a free sector e.g. a spare sector is reached. Otherwise, adiscontinuity in the logical to physical mapping exists as it is thecase e.g. when a sector is allocated to a replacement sector.

The sole allocation process of a defective sector without re-allocationas conventionally practised causes an extra delay in service time of adisc drive. When the drive 1 encounters a defective sector and decidesto allocate it to a remote spare sector 16, the head 3 is moved from thetrack with the defective sector in the user area to a track where sparesectors are allocated in a remote spare area 16. When the right sparesector is rotated under the read/write-head 3, the data is written tothe spare sector. Subsequent, if the drive has to resume reading orwriting, the head is moved back to the original track 8 where thedefective sector was found. This process costs extra time due tosearching and accessing the sector allocated in the remote spare area16: the head 3 has to move to the spare sector in a remote spare area 16to read or write at the spare sector and the head 3 has to move back toresume reading or writing. In a real-time audio-video applicationtherefore, conventional methods for handling data and a conventionaldata storage apparatus may not guarantee a maximum service time in casean error occurs. Alternatively delivering erroneous or incomplete datato the host and reporting the error has to be taken into account. Whenaccessing a data pool with one or more erroneous sectors, the drive willalso be unable to finish the request within the maximum service time.

FIG. 4 illustrates an example according to a preferred embodiment how toconvert sectors allocated in a spare area SA of spare sectors S intoslipped or skipped sectors in the user area UA and to thereby prevent adelay in request service times. The skip and slip scheme is applied forre-allocation during use of the disc drive for grown defects B. Thesectors are re-allocated into a contiguous free region of sectors F. Thespare area SA may be a remote spare area 16 of FIGS. 1 and 2 a or aspare area SA assigned to essentially each track as depicted in FIG. 6or a spare area S assigned to an allocation unit, in particularessentially each allocation unit, as depicted in FIG. 7. This schemerelies on the idea that slipped sectors compared to sectors, which areallocated in remote spare areas 16, cause much less or nearly negligibleperformance loss. According to the proposed concept it is possible toguarantee request service times in particular for audio-videoapplications. This is true even if access is made to a data pool thatcontained sectors allocated in a remote spare area as these sectors arere-allocated into contiguous free regions of sectors F in the user areaUA.

In detail the proposed concept works according to a preferred embodimentas follows.

As outlined above a discontinuity in the logical to physical mapping mayexist. This is the case when a sector is allocated in a remote sparearea 16. Such discontinuity in the mapping is referred to as a “bubble”.Therefore, in case of an allocation of a defect sector to a remote sparearea 16 a bubble has only moved towards a spare area and still continuesto exist. The bubble disappears only if it reaches a free area with asufficient number of free sectors. Such free area is provided in thepreferred embodiment according to the proposed concept.

In the example of FIG. 4 only a fabrication defect may be provided onlyonce by the slipping of sectors during manufacturing due to a defectsector at the physical block address PBA 15. This is referred to by B asthe bad sector in the first row of FIG. 4 at logical block address LBA15.

Further a grown defect may occur as indicated by B for a further growndefect at PBA 2 in the second row of FIG. 4. The corresponding data ofthe grown defect labelled with logical block address LBA 2 may beallocated and mapped into a spare area as indicated by “2” in the secondrow of PBA 10 of FIG. 4. In a further step information is provided aboutthe size of a contiguous free region in the user area as indicated by Fat PBA 1, PBA 3 and PBA 4 in the third row of FIG. 4. Such informationis advantageously provided by the host to the drive and preferablydeclares the largest consecutive free area and not just the newly freedup area. This means that the hard disc drive does not have to keep trackof a free list for the entire disc. As shown in the third row of FIG. 4the drive uses this information to re-allocate logical sectors: there-mapped sector LBA 2 is slipped and at the end of the free area a newtype of bubble sector appears where the slipping stops and is stillre-mapped. As soon as the application declares a new free area thatoverlaps the bubble, the bubble will be moved to the end of that area asindicated in row 4 of FIG. 4. This is repeated until finally theapplication declares a free area that allows the bubble to move into acontiguous free region with sufficient size in the user area asindicated in row 5 of FIG. 4. At that time the grown defect B haschanged into regular slipped sectors that cause much less performanceloss than a re-mapped or replaced sector.

Advantageously the bubble tends to cause much less performance loss thana re-mapped sector, because in practice the re-mapping of the bubblewill happen at the end of an allocation unit. For a bubble the hard discdrive can always move to the re-mapped location of the bubble at the endof a regular data transfer.

The concept as outlined in FIG. 4 works best when disc space is useddynamically; the bubble may only move to a free region when there aresufficient many “free”-declarations, in particular sufficient manyoverlapping “free”-declarations. In particular the concept proposedworks well in applications like those for personal video recorders, e.g.applications like those of the TiVo company. Applications of thementioned kind usually comprise a service containing e.g. an electronicprogram guide to keep track of a preferred program profile. For suchpurpose a data storage apparatus, like a hard disc drive or a DVD, or amethod of handling data on a data storage medium of the proposed kind isparticular favourable. This is because for applications of the mentionedkind most of the disc content is refreshed in the course of a few days.

It is to be noticed that a bubble takes the same extra data storagecapacity as a slipped or re-mapped sector. On the other hand it needsone extra item of administration for the current location of the bubblei.e. the end of the “free”-declaration.

Advantageously it is possible for the hard disc drive to also definedownward bubbles that move downwards towards a re-mapped defect or anupward bubble as described above. When the downward bubble meets are-mapped defect or on upward bubble, they annihilate into a singleslipped sector. This would improve the statistics of actually reachingthe slipped state. On the other hand the downward bubble takes up anextra spare sector during its life, and requires some extraadministration.

Even in a scheme where special audio video commands will never accessthe re-mapped sectors, the bubble scheme is advantageous: aconventionally re-mapped sector corresponds to an error that is alwayson the same place. Converting it into a bubble makes the erroradvantageously move towards the end of a free area. Thereby new errorscould be bubbled e.g. into a single lost cluster. As the bubbles movefurther upward, they will evaporate in the hard disc drive's free area.Extra measures, like protocol etc., are provided on the host's side tomake this a guaranteed scheme. Even in a simple approach the proposedconcept help in gradually sweeping the system clean.

A simple error-report mechanism that informs the host about theresulting logical bad sectors after the free command is advantageouslyapplied. If a hard disc drive's spare area should be happened to befully loaded the disc can in such a case only declare sectors to be bad.This is where the bubble-slip scheme is still advantageous. It providesa mechanism to sweep multiple bad sectors to a single logical addressarea which can then be avoided by the host. Again an error reportmechanism after the free command is preferred.

Advantageously the above scheme makes the drive responsible for thework. It has the full knowledge about defect management. The only thingit may need is the free information from the host and the new concept ofthe bubble to make it work.

The host's file system could do a very similar same thing, and actuallyreserve or create more spare area if needed. The minimum requirement maybe that the host can find out about the hard disc drives re-mappedsectors, best in a standardised way. The simplest approach would be thento never reuse a cluster with a re-mapped sector in it. Conventionallythis may be rather costly of audio video systems with a typical clustersize of hundreds, thousands or even ten-thousands of sectors. To avoidsuch gross space loss, several schemes can be implemented, includingbubble-like approaches as outlined above. The proposed method alwaysprovides an efficient mechanism to skip bad or re-mapped sectors inlarge requests.

Cutting a large request into smaller ones is possible but may haveperformance penalties similar to those related to current 128 Kbyterequest size limitation. The alternative is to add a mechanism to informthe disc that known bad sectors should be excluded in the future.Preferably this is initiated on a sector by sector basis by the host,because also for the host the slip schemes are only easy in a free area.The advantage of this approach is that the host can easily create morespare areas. The need for slightly more protocol between a host and ahard disc drive is only a small disadvantage.

In FIG. 5 a bubble defect management combined with a track-based sparingis illustrated as a further preferred embodiment. In combination withabove described scheme a spare area array SA of a number of sparesectors may be provided on essentially each track 8 as further shown inFIG. 6 a and FIG. 6 b. Thereby, advantageously full spare areas may bepartly or completely be freed. As exemplified in the first row of FIG. 5the physical sectors with PBA 3 and PBA 4 are re-allocated to the sparesectors of PBA 6 and PBA 7 respectively. Thereafter the sectors areslipped and the spare sector of PBA 7 is freed. According to theproposed embodiment a sector of PBA 13 in a spare area array is usedinstead.

Reserving spare sectors on each track means sacrificing drive capacityand performance. Because there will be less sectors per track, the dataread or written on each disc rotation will also be less. So it isdesirable to have as few spare sectors as possible on each track. On theother hand it is undesirable to have all the spare sectors on a trackoccupied. In this case a further grown defect would have been to bere-allocated to a spare sector on another track which would cause aperformance loss and the request service time would again not beguaranteed. Again in such a case the conversion of re-allocated sectorsinto slipped sectors according to the proposed concept may be done asdescribed above. To remove the small disadvantage of an extra protocolbetween the host and the drive and extra administration for the bubblescreated as outlined above the conversion could also be doneautomatically. The extra free information from the host would becomeunnecessary as will be outlined for a further preferred embodiment.

In audio-video applications, a block of several megabytes is transferredat each disc access. Such a block includes a number of tracks. Forexample a block of 4 MB includes more than 10 tracks on a current harddisc drive with 800 sectors per track on the outer diameter. Since thereare spare sectors on each track or allocation unit the drive can slipany sectors allocated to remote spare area by re-allocation within thereach of each write access. This way the slipping of the re-allocatedsectors can be done automatically without the intervention of the host.Furthermore, this can be done on-the-fly, since the logical to physicaladdress mapping is essentially done in the hard disc drive controller.Even if there are no spare sectors in the reach of each write access,the conversion can still be done automatically. The consequence is thenthat bubbles are introduced in the system.

In general, conversion of re-allocated sectors into slipped sectors canbe used to free spare area SA when there are a number of spare areas SA,S distributed over the disc, as for example shown in FIGS. 6 a and 6 band anyone of them gets full.

A grown defect is advantageously re-allocated to the nearest availablespare sector SA, S.

Advantageously spare sectors SA on each track 8 a, 8 b are allocated inadvance of a start sector 20 a, 20 b or a servo wedge and a track skew18 is extended respectively as depicted by reference mark 28 in FIG. 6b. The curved dashed line 21 in FIG. 6 b shows the motion 21 of theread/write-head of the disc drive during a track switch. This shows thatupon a track switch 21 from track n the head 3 is settled already on thenew track n+1 to read or write the spare sectors 22 b and the startsectors 20 b due to the extended track skew 28. The spare sectors 22 aof track n are in advance of start sectors 20 a or a servo wedge.

A grown defect is preferably re-allocated to the nearest available sparesector SA. When a grown defect must be re-allocated further away,because the nearest spare area is occupied, the correspondingperformance loss is slightly larger.

Even still then a mechanism as outlined above is advantageously appliedespecially in a real-time application to free spare space when a sparearea SA gets full.

As conventional hard disc drives incorporate the logical block addressesinto an error correction code at least a part of a disc must beoverwritten if any changes are made in the logical to physical addressmapping of the drive must be updated accordingly because the errorcorrection code (ECC) of each sector. Therefore, advantageously to applythe above scheme physical addresses, in particular physical blockaddresses are used in the error correction code (ECC) instead of logicalblock addresses.

While there has been shown and described what is considered to bepreferred embodiments of the invention it will of course be understoodthat various modifications and changes in form or detail could readilybe made without departing from the spirit of the invention. It istherefore intended that the invention may not be limited to the exactform or detail herein shown and described nor to anything less than thewhole of the invention herein disclosed and as herein after claimed.

1. Data storage apparatus (1) comprising a data storage medium (2), inparticular a disc drive (1) comprising a data storage disc (2) formattedin a predetermined format architecture comprising a plurality of atleast one format feature, in particular selected from the groupconsisting of: zones, cylinders and tracks, and having a user area and aspare area defined thereon, characterised in that the formatarchitecture provides a plurality of spare area arrays, each of thespare area arrays being respectively assigned to essentially each of theplurality of the at least one format feature.
 2. Data storage apparatusas claimed in claim 1, characterised in that the format architectureprovides a plurality of spare area arrays (SA, 22 a, 22 b), wherein eachof the spare area arrays (SA, 22 a, 22 b) are respectively assigned toessentially each of a plurality of tracks (8).
 3. Data storage apparatusas claimed in claim 1 characterised in that the apparatus (1) furthercomprises a read/write-head (3), a drive to rotate the medium and aservo to move the head, a controller (6) having a control electronics, amicroprocessor and a memory (RAM, ROM) and an interface for connectingthe apparatus (1) to a host (7).
 4. Apparatus for reproducingaudiovisual information, comprising a data storage apparatus, the datastorage apparatus comprising: a data storage medium (2), in particular adisc drive (1) comprising a data storage disc (2) formatted in apredetermined format architecture comprising a plurality of at least oneformat feature, in particular selected from the group consisting of:zones, cylinders and tracks, and having a user area and a spare areadefined thereon, wherein the format architecture provides a plurality ofspare area arrays, each of the spare area arrays being respectivelyassigned to essentially each of the plurality of the at least one formatfeature.